MIL-HDBK-1022A
8.6.4
Tank Bottoms. Slope the tank bottoms downward from
the shell toward a sump at the center. A slope of 5 percent
is required for positive drainage and self-cleaning action for
tanks storing aviation turbine fuels. After the tank
hydrostatic test, test the tank bottom by a helium leak
detection identification method in accordance with the Air
Force standard design prior to tank coating. Conduct all
tests recommended by API Std 650.
8.6.5
Foundations. Design tank foundations on the basis
of a soils exploration program including preliminary
exploration as a minimum and detailed exploration and testing,
if existing soil data is not available and/or inadequate.
Refer to NAVFAC DM-7.01 and Army Corps of Engineers AEI.
Analyze the results of the exploration program to determine
the most practical and economical design to provide a stable
foundation for the tank. See Facility Plate No. 014. As a
minimum, use the following criteria for all tank designs:
a) Prevent external corrosion of tank bottoms by
locating the tanks well above the general tank field grade,
provide adequate tank field drainage away from the tank, and
construct the foundation pad of clean, free-draining granular
material. If sand is used, ensure a minimum electrical
conductivity of 50,000 ohm-cm. Foundation material should be
neutral or alkaline with a pH greater than 6.5, a chloride
concentration less than 300 ppm, and a sulfate concentration
less than 1,000 ppm as specified by API RP 651. The sand may
be washed and the pH may be raised to meet the requirements.
Include cathodic protection to prevent external corrosion of
the tank bottoms. Do not use oil in the sand under the tank,
unless local and state regulations concur with its use. Do not
use dredge material or beach sand.
b) Provide good drainage under the tank.
c) Provide a reinforced concrete ringwall foundation
and secondary containment. Locate the tank bottom a minimum
of 12 inches (300 mm) above the dike basin.
d) Cover the area beneath the tanks with a dike
fuel-impermeable liner complying with Standard Design AW
78-24-27 and meeting local and state requirements. Install
all liners according to the manufacturer's requirements.
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